Various methods and systems for construction of three-dimensional models or objects have been developed for a number of applications, including the rapid fabrication of prototypes and the low volume fabrication of models and objects of varying degrees of complexity.
The need for rapid, low cost, low volume fabrication of models and parts has generally been met by various three-dimensional (3D) modeling processes that employ layer by layer building processes. According to typical 3D modeling processes of the prior art, a model or a part is built up by the successive deposition of layers generally comprising a “model” material, forming the final part to be manufactured, and a sacrificial material that provides support for the model material during the building process. Following completion of the fabrication process, the sacrificial material is subsequently removed thereby leaving the model material which forms the final part to be manufactured.
Typical examples of 3D modeling processes of the prior art include, for example, Householder, U.S. Pat. No. 4,247,508, which describes a modeling process that employs two substances, one a fill material and the other a mold material, that are deposited layer by layer to build an article. The two materials in each layer are not in contact with each other while the layer is being formed because Householder '508 uses a grid to separate the two materials as they are being deposited. After the materials in each layer are deposited, the grid is moved to the next layer so that the two materials may fill the space left by the removed grid and thereafter solidify in contact with each other in the same layer.
Helinski, U.S. Pat. No. 5,136,515, describes a method wherein a three-dimensional model is produced layer by layer by jetting droplets of at least two solidifiable materials, one material forming the article and a second material forming a support for the article. The second material is subsequently removed by heating, cutting, melting, chemical reacting, and so on, to leave the desired article.
Penn, U.S. Pat. No. 5,260,009, describes a system and process for making three-dimensional objects by dispensing layer upon layer of modeling material using an inkjet which is turned “on” or “off” according to a two dimensional data map of each layer of the object. The two dimensional data map is stored and relayed by a microprocessor and defines locations on a matrix at which printing is to occur in a manner such as is used in printing images using raster scan printing.
Sanders, Jr. et al., U.S. Pat. No. 5,506,607, describes a system for building three-dimensional models by vector plotting layer-upon-layer applications of solidifiable substances. The layers are formed by expelling minuscule beads of the substances in a liquid or flowable phase onto a platform from one or more jets wherein the jets and platform are relatively movable in the X, Y and Z coordinate system and the beads are deposited along vectors during X-Y relative movement.
Sanders, Jr. et al., U.S. Pat. No. 5,740,051, describes a method and apparatus for producing a three-dimensional model by forming a continuous plurality of parallel layers of modeling material by repeatedly producing a plurality of bead producing drops of the modeling material for deposition at desired locations, controlling the locations and timing of deposition to produce vectors in any and all directions required to produce an outer surface defining a wall of a layer with a desired surface finish, and adjusting the distance of the location of drop production to the location of drop deposition in preparation for the formation of a subsequent layer.
Penn et al., U.S. Pat. No. 6,175,422, describes a method and process for computer-controlled manufacture of three-dimensional objects by dispensing a layer of a first insoluble material, such as a liquid, onto a platform at predetermined locations corresponding to a cross-section of the object, which then hardens. A second material, preferably water soluble, is then sprayed onto this layer to thereby encapsulate the hardened insoluble material. The uppermost surface of this encapsulant is planed, thus removing a portion of the encapsulant to expose the underlying insoluble material for a new pattern deposition. After any resulting planing residue is removed, another layer of liquid, insoluble material is dispensed onto the planed surface. The insoluble material can be of any color and may vary from layer to layer, and from location within a layer to location with a layer. These steps are repeated, until the desired three-dimensional object, encapsulated in the soluble material, is completed. At this point, the object is either heated or immersed in solvent, thereby dissolving the soluble material and leaving the three-dimensional object intact.
Other systems and methods of the prior are described, for example, in U.S. Patent Publication No. 2009/0252821 which relates to a method of fabricating a model by deposition of a model material and a sacrificial material in layers wherein the sacrificial material which defines the bounds of the model is deposited drop by drop and the model material is deposited at high speed by spraying, while U.S. Patent Publication No. 2010/0021638 additionally describes the use of a third material to construct the layers and U.S. Pat. No. 6,019,814—relates to the use of a nozzleless, ultrasonic device for the sequential deposition of the materials.
U.S. Patent Publication No. 2005/087897 relates to a variation of the basic method for constructing a model by deposition of successive layers of a model material comprising the model and shell material enclosing the model material wherein certain layers may be deposited as partial layers to reduce the volume of material to removed when each layer is planed and to permit the construction of more complex geometries in the layers.
U.S. Pat. No. 5,209,878 relates to the use of either thin partial layers of material or a material capable forming a meniscus in the edge regions between successive layers of different dimensions to reduce or eliminate “stairstep” voids created at the edges of layers having different dimensions.
U.S. Patent Publication No. 2002/0129485 describes a system which is an agglomeration of previously known systems for fabricating three-dimensional objects which thereby provides a very flexible but complex system capable of achieving features of a wide variety of methods.
Other prior art systems employ methods somewhat analogous to those used to construct three-dimensional objects as successive layers of different materials, but are adapted specifically and essentially to object molding processes. For example, U.S. Patent Publication No. 2004/0089980 describes a method for fabricating three-dimensional models by deposition and machining of three or four successive thick layers, thereby concurrently forming a mold for the object and the object itself. The layers include including a first additive (non-sacrificial) layer which is machined to define the bottom contour of a next layer, which is a second additive (non-sacrificial) layer. The second additive (non-sacrificial) layer is deposited on the first subtractive (sacrificial) layer and machined to define the upper contour of the second additive (non-sacrificial) layer, which is the top of the finished model, with a second subtractive (sacrificial) layer being deposited and machined, if desired. The subtractive (sacrificial) material is removed when all layers are completed, thereby leaving a model formed of the additive (non-sacrificial) material.
U.S. Pat. No. 7,003,864 describes a method that is generally similar to that described in U.S. Patent Publication No. 2004/0089980 in depositing and machining three layers which concurrently form a mold for an object and the object itself, including depositing and planing a base layer of support material, depositing and removing regions of a second layer to form a mold of the part, adding a construction material to the removed regions of the second layer, and planing or machining the support and construction materials of the second layer.
Following manufacture of a three-dimensional composite model, comprising both the sacrificial material and the model material, it becomes necessary to separate and remove the sacrificial material from the model material to thereby obtain the desired three-dimensional model. During such removal process, the three-dimensional composite model is first removed from the manufacturing table or other support platform upon which the three-dimensional composite model was fabricated, and this is typically achieved by use of either heat (e.g., heating the surface of the manufacturing table or other support platform) or a conventional solvent. Next, the sacrificial material must be removed and separated from the model material to thereby obtain the desired three-dimensional model and such removal and separation is typically achieved by a dewaxing process, i.e., the process for removing the sacrificial material from the model material.
One currently utilized dewaxing process involves placing the fabricated three-dimensional composite model, following removal from the manufacturing table or other support platform, in a heated (VSO) bath, at a temperature of about 55° C., for approximately 45 minutes in order to dissolve and melt away the sacrificial material from the model material. As is known in the art, this conventional dewaxing process does not work very efficiently without increasing or elevating the temperature of the bath. As the temperature of the bath is elevated, the rate at which the sacrificial material dissolved away from the three-dimensional composite model is consequentially increased and this leads to a much faster and expedited separation of the sacrificial material from the model material and thereby the final three-dimensional model.
During such dewaxing process, the inventors found that some fragile models had hairline cracks and fractures as well as other breaks which detracted from the overall quality of the final three-dimensional model which typically leads to the unacceptability of the final three-dimensional model. The inventors have also noted that this problem is particularly problematic with three-dimensional models which have either one or more very thin wall(s) or thin section(s), one or more fine detail(s) or feature(s) or one or more intricate component(s) or element(s). In the event that the final three-dimensional model is deemed unacceptable, then the manufacturing process to obtain the unacceptable three-dimensional model must be refabricated and this, in turn, leads to lost manufacturing time and added expenses and is to be avoided.
As a result of closely examining the hairline crack(s), fracture(s), break(s), flaw(s) and/or other imperfection(s) that sometimes occur in three-dimensional models, the inventors believe that such flaws and imperfections are occurring as a result of one or more of the following factors. That is, the inventors believe that such flaws and imperfections occur because of either a higher coefficient of thermal expansion for the sacrificial material than for the model material, the differences in thermal conductivity between the sacrificial material and the model material and/or the propensity of the sacrificial material to carry or transmit stress throughout the composite model to the final three-dimensional model.
The current methods and systems of the prior art, for fabricating three-dimensional models and objects, however, each have a significant number of fundamental problems as briefly discussed above.